The present invention relates to a device for monitoring the intraocular pressure (IOP). The present invention relates in particular to a device that can be placed on the eye of a user to monitor intraocular pressure over an extended period of time, for example 24 hours or more. The present invention also relates to a kit and to a system for monitoring the intraocular pressure (IOP).
Glaucoma is a widespread disease characterized by an elevated intraocular pressure (IOP). This elevated IOP produces a gradual loss of peripheral vision. There is therefore a need to have a detailed knowledge of IOP in glaucoma patients in order to provide reliable diagnostics or for setting up new therapies.
Patent EP1401327 describes an intraocular pressure recording system comprising a soft contact lens and a pressure sensor fixed to the contact lens. The pressure sensor comprises an active strain gage which is located around the center of the contact lens, thus allowing measuring the spherical deformations of the eyeball that are due to IOP changes. In one embodiment, the pressure sensor comprises two active strain gages and two passive gages placed in a Wheatstone bridge configuration. The active strain gages are circular gages situated around the center of the contact lens, while the passive gages are placed essentially radially to the lens in order to minimize their deformation when the eyeball is deformed. The passive gages are made of several radial segments located on one side of the contact lens, which are interconnected by short and substantially tangential segments.
A drawback of this intraocular pressure recording system is that it is difficult to optimize the characteristics of the sensor without compromising the comfort of the user. For the passive gage to be as insensitive as possible to the deformations of the eyeballs, the radial segments should be as long as possible relative to the tangential segments. However their length is limited because if they reach too close to the center of the lens they lay within the sight of the user. And even if the length of the radial segments is correctly limited for a standard use of the contact lens, one can't exclude situations where the user's sight might be disturbed by the passive gages, for example if the contact lens accidentally only slightly slides on the eye, or in a dark environment, where the user's pupil is particularly dilated.
Another drawback of this intraocular pressure recording system is that the asymmetrical design of the passive gages relative to the center of the contact lens could lead to asymmetrical temporary or permanent deformations of the contact lens itself, which might then loose its spherical shape, thus resulting in discomfort for the user wearing the lens.
Still another drawback of the intraocular pressure recording system of EP1401327 is that the position and the shape of the passive gages are very different from those of the active strain gages. The influence of variations in environmental factors other than the IOP, for example of the temperature, the humidity, etc., on the physical properties of the passive gages might therefore differ significantly from the influence of the same variations on the physical properties of the active strain gages, thus inducing errors or inaccuracies when determining the IOP.